Battery pack system

ABSTRACT

A battery pack system is disclosed. The battery pack system includes a battery pack having batteries arranged in a plurality of parallel groups that are connected in series. Each parallel group includes a plurality of the batteries connected in parallel. The electronics are configured to drop the current at which the battery pack is operating from a first current level to a second current level one or more times. The second current level is lower than the first current level. The electronics can drop the current from the first current level to the second current level during the charge and/or discharge of the battery pack. In some instances, the electronics intermittently drop the current from the first current level to the second current level during the charge and/or discharge of the battery pack.

RELATED APPLICATIONS

This Application is a continuation of U.S. patent application Ser. No.11/603,757, filed on Nov. 22, 2006, now U.S. Pat. No. 7,573,234 entitled“Battery Pack System,” which claims the benefit of Provisional U.S.Patent Application Ser. No. 60/740,204, filed on Nov. 28, 2005, entitled“Battery Pack System” and also of Provisional U.S. Patent ApplicationSer. No. 60/753,862, filed on Dec. 22, 2005, entitled “Battery PackSystem,” each of which is incorporated herein in its entirety.

FIELD

The present invention relates to power sources and more particularly tointerconnection of multiple power sources.

BACKGROUND

As batteries play a larger role in powering the movement of vehiclessuch as cars, systems that employ a plurality of batteries have beendesigned. Different batteries will have different capacities, differentself-discharge rates and/or different impedances that will affect theperformance of these systems. For instance, drawing a high current fromthese systems can cause the voltage of one or more batteries to fall toa dangerously low level and fail while the remaining batteries remainoperational. The failure of the battery can cause failure of the entiresystem. Because prior systems have not adequately addressed thevariations in the performance of different batteries there is a need foran improved battery system.

SUMMARY

A battery pack system is disclosed. The battery pack system includes abattery pack having batteries arranged in a plurality of parallel groupsthat are connected in series. Each parallel group includes a pluralityof the batteries connected in parallel. The electronics are configuredto drop the current at which the battery pack is operating from a firstcurrent level to a second current level one or more times. The secondcurrent level is lower than the first current level. The electronics candrop the current from the first current level to the second currentlevel during the charge and/or discharge of the battery pack. In someinstances, the electronics intermittently drop the current from thefirst current level to the second current level during the charge and/ordischarge of the battery pack.

Another embodiment of the battery pack system includes a pack assemblyhaving a plurality of battery packs connected in a plurality of systemparallel groups and in a plurality of system series groups. Each systemparallel group includes a plurality of battery packs connected inparallel. Each system series group connects in series a battery packfrom each of the system parallel groups. The electronics are configuredto intermittently drop the current at which the pack assembly isoperating from a first current level to a second current level. Thesecond current level is lower than the first current level. Theelectronics can intermittently drop the current from the first currentlevel to the second current level during the charge and/or discharge ofthe battery pack. In some instances, the battery packs have batteriesarranged in a plurality of parallel groups and a plurality of seriesgroups.

During discharge of the battery pack system, the second current levelcan be below a recharge current at which battery packs in the samesystem parallel group can recharge one another or below a current levelat which batteries in the same system parallel group can recharge oneanother. In some instances, the electronics are configured to stopintermittently dropping the current from the first current level to thesecond current level when the first current level falls below therecharge current. Additionally or alternately, the electronics can beconfigured to stop intermittently dropping the current from the firstcurrent level to the second current level when the current level risesabove a threshold associated with high power applications.

Methods of operating and controlling the battery pack systems are alsodisclosed.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a schematic diagram of a battery pack system. The batterypack system includes electronics configured to control the charge and/ordischarge of a battery pack.

FIG. 1B is an alternate schematic for the batteries in the battery packof FIG. 1A.

FIG. 1C is a schematic diagram of the battery pack of FIG. 1A where afuse is positioned in series with each of the batteries.

FIG. 1D illustrates a possible plot of pack current versus time for adischarging battery pack.

FIG. 2A is a schematic for a battery pack system that includes aplurality of battery packs. The battery pack system includes acontroller in electrical communication with a pack assembly.

FIG. 2B is a schematic for a pack assembly that includes both high powersources and low power sources.

FIG. 2C illustrates a possible plot of pack current versus time for adischarging battery pack assembly.

FIG. 3 illustrates a battery pack system employed in a vehicle.

DESCRIPTION

The battery pack system includes electronics in electrical communicationwith a battery pack. The battery pack includes electronics configured tocontrol the charge and discharge of a battery system. The battery systemcan include batteries arranged in a plurality of parallel groups and ina plurality of series groups. Each parallel group includes a pluralityof batteries connected in parallel. Each series group connects in seriesa battery from each of the parallel groups. During periods of rapiddischarge, different batteries in the same parallel group may havedifferent levels of voltage drop. As a result, the voltage of one ormore of the batteries in a parallel group can fall to a dangerously lowlevel that can cause the battery to fail while the other batteries inthe same parallel group remain intact. The opposite situation can occurduring charging. For instance, one or more of the batteries can becharged to a dangerously high voltage. These voltage differences can bea result of capacity, self-discharge and/or impedance differentialsbetween the different batteries. These differences can be present duringthe first discharge of the battery pack system or may develop over time.

During periods of low pack current, one or more batteries in a parallelgroup will recharge other batteries in the same parallel group untileach battery in the parallel group has about the same voltage. Theelectronics can be configured to take advantage of this rechargecapability. For instance, the electronics can be configured tointermittently drop the current from a first current level to a secondcurrent level. The first current level can be a current level at whichvoltage differentials can be generated between different batteries inone or more of the parallel groups and the second current level can be alevel at which batteries in the same parallel group can recharge oneanother. As a result, the intermittent current drop provides thebatteries with an opportunity to equalize their voltage.

The battery pack can also be one of a plurality of battery packs in thebattery pack system. The battery pack system can include a controllerconfigured to control the charge and/or discharge of a pack system. Thepack system can include a plurality of battery packs arranged in aplurality of system parallel groups and in a plurality of system seriesgroups. Each system parallel group includes a plurality of battery packsconnected in parallel. Each system series group connects in series abattery pack from each of the system parallel groups. During periods ofrapid discharge of the battery pack system, different battery packs inthe same system parallel group may have different levels of voltagedrop. As a result, the voltage of one or more of the battery packs in asystem parallel group can fall to a dangerously low level that can causethe battery pack to fail while the other battery packs in the samesystem parallel group remain intact. The opposite situation can occurduring charging. For instance, one or more of the battery packs can becharged to a dangerously high voltage. These voltage differences in asystem parallel can be a result of capacity, self-discharge and/orimpedance differentials between the different battery packs in thesystem parallel group.

During periods of low pack current, one or more battery packs in asystem parallel group will recharge other batter packs in the samesystem parallel group until each battery pack in the system parallelgroup has about the same voltage. The controller can be configured totake advantage of this recharge capability. For instance, the controllercan be configured to intermittently drop the system current from a firstcurrent level to a second current level. The first pack system currentlevel can be a current level at which voltage differentials can begenerated between different batteries in one or more of the parallelgroups and the second pack system current level can be a level at whichbatter packs in the same parallel group can recharge one another. As aresult, the intermittent current drop provides the battery packs with anopportunity to equalize their voltage.

FIG. 1A is a schematic diagram of battery pack. The battery packincludes electronics 8 in electrical communication with a battery system10. The electronics 8 are in electrical communication with a firstterminal 5 and a second terminal 6. The first terminal 5 and a secondterminal 6 serve as the terminals for the battery pack.

The battery system 10 includes two primary parallel lines 12 thatconnect three series groups 14 in parallel. The series groups 14 eachinclude three batteries 16 connected in series. Primary series lines 18each provide electrical communication between a series group 14 and aprimary parallel line 12 and secondary series lines 20 provideelectrical communication between the batteries 16 connected in series.

The battery system 10 also includes a plurality of secondary parallellines 22. The secondary parallel lines 22 each include one or more crosslines 24 that provide electrical communication between the secondaryseries lines 20 in different series groups 14. Accordingly, eachsecondary parallel line 22 provides a parallel connection between thebatteries 16 in different series group 14. For instance, each secondaryparallel line 22 provides electrical communication between differentseries groups 14 such that a battery 16 in one of the series groups 14is connected in parallel with a battery 16 in the other series groups14. Because a single secondary parallel line 22 only provides one of theparallel connections, another connection is needed to connect batteries16 in parallel. The other parallel connection can be provided by anothersecondary parallel line 22 or by a primary parallel line 12. Each of thebatteries 16 connected in parallel belongs to a parallel group 28.Accordingly, the battery system 10 of FIG. 1A includes three parallelgroups 28.

The battery system 10 of FIG. 1A can be scaled to include more batteriesor fewer batteries. For instance, the battery system 10 can include fouror more batteries, twelve or more batteries, twenty-five or morebatteries, eighty-one or more batteries, one hundred or more batteries.The number of batteries in each parallel group can be the same ordifferent from the number of batteries in each series group 14. Thenumber of batteries in each series group 14 can be increased in order toincrease the voltage of the system or decreased in order to decrease thevoltage of the system. Each series group 14 can include two or morebatteries; four or more batteries; more than eight batteries; or fifteenor more batteries. The number of series groups 14 can be increased forapplications that require higher power levels or decreased forapplications that require lower power levels. In one embodiment, thebattery pack includes only one parallel group and no series groups. Thebattery pack can include two or more series groups; four or more seriesgroups; ten or more series groups; or fifteen or more series groups 70.

The connections between the batteries can be standard methods forconnecting batteries. The connections between the batteries and theconductors can be made using connection methods that are suitable forthe amount of current and power that will be delivered by the battery.For instance, conductors can be connected to a battery by welding.Additionally or alternately, one or more of the primary parallel linesand the connected primary series lines can optionally be integrated intoa single line. For instance, a single wire, cable, piece of sheet metal,or metal bar can serve as both a primary parallel line and as theconnected primary series lines. Additionally or alternately, one or morethe secondary parallel lines and the connected secondary series linescan optionally be integrated into a single line. For instance, a singlewire, cable, piece of sheet metal, or metal bar can serve as both asecondary parallel line and as the connected secondary series lines.

The battery system 10 can include one or more shunt circuits connectedin parallel with a parallel group. A shunt circuit can include one ormore switches and one or more resistors. For instance, the battery packof FIG. 1A includes a plurality of shunt circuits 29 that are eachconfigured to provide a current pathway around a parallel group. Eachshunt circuit 29 includes a switch 30 connected in series with one ormore resistors 31. The switches can be operated by the electronics. Eachswitch 30 is arranged such that one of the parallel groups is shortedwhen the switch is closed and but the shunt circuit is an open circuitwhen the switch is open. Accordingly, the parallel group is not shuntedwhen switch is open. When a switch is closed, the associated resistor isselected to prevent the functioning batteries in the bypassed parallelgroup from being short circuited.

The electronics 8 include a current controller for controlling the packcurrent. For instance, the electronics 8 can include a pulse generatorconfigured to generate a signal that intermittently drops the packcurrent from the first current level to the second current level. In oneexample, the current controller includes one or more switches that dropthe pack current to a zero current or an open circuit current when theswitch is open. Closing the switch can return the pack current to thefirst current level. The switch can be opened and closed tointermittently drop the current to the second current level. In anotherexample, the current controller can include a switch in parallel withone or more resistors including variable resistors. When the switch isopen the pack current will be dropped to a current limited by the one ormore resistors. The resistors can be adjusted such that when the switchis open, the pack current is dropped to a second current level. When theswitch is open, the one or more resistors are bypassed and the packcurrent rises to the first current level.

Although FIG. 1A illustrates the secondary parallel lines 22 providingelectrical communication between the series groups 14 such that abattery 16 in one of the series groups 14 is connected in parallel witha battery 16 in each of the other series groups 14, the secondaryparallel lines 22 can provide electrical communication between theseries groups 14 such that a battery 16 in one of the series groups 14is connected in parallel with a battery 16 in a portion of the otherseries groups 14.

The battery assembly of FIG. 1A can also be illustrated as a pluralityof parallel groups connected in series as shown in FIG. 1B. In FIG. 1B,two parallel lines 31 connected by a series line 33 replace thesecondary parallel lines of FIG. 1A. The construction of the batteryassembly shown in FIG. 1A may be preferable because all of the packcurrent must pass through the series lines of FIG. 3B. As a result, theseries lines may need to be larger than other lines in the battery packand accordingly may add weight to the battery pack.

The battery system 10 can include battery disconnection devices inseries with the batteries. The battery disconnection devices candisconnect a battery from the battery system 10 to stop or reducecurrent flow through a battery to prevent damage to the battery or tothe battery system 10. The battery disconnection devices can addressundesirable increases in pressure in the battery, undesirable increasesin the temperature of a battery, or undesirable current levels through abattery.

Suitable battery disconnection devices for addressing undesirablepressure increases in a battery include current interruption devicesand/or burst discs. Current interruption devices are often integratedinto a battery and include a diaphragm that deforms when the pressure ina battery rises above a threshold. The deformation of the diaphragmdisrupts an electrical connection in the battery and accordinglydisconnects the battery from the battery system.

Suitable battery disconnection devices for addressing undesirablepressure increases in a battery include positive temperature coefficient(PTC) resistors. A PTC resistor usually includes a material withtemperature dependent electrical conductivity. For instance, theconductivity of the PTC material can decrease as the temperatureincreases. As a result, the current through the battery decreases as thebattery temperature decreases. A PTC material can be coated between theactive material and the substrate in an electrode or mixed in a slurrywith the active material and coated on the substrate along with theactive material. Additionally or alternately, the material can beemployed as any of the other current carrying battery connections.Examples of a material suitable for use as a PTC include, but are notlimited to, high-density polyethylene (melting point: 130 to140.degree.), low-density polyethylene (melting point: 110 to112.degree. C.), a polyurethane elastomer (melting point:140-160.degree. C.), and polyvinyl chloride (melting point: about145.degree. C.). Another suitable battery disconnection devices foraddressing undesirable temperature increases in a battery includeelectronics for disconnecting the battery in response to temperatureincreases. For instance, the electronics can employ a temperaturemeasuring device to monitor the temperature of the battery and a switchto disconnect the battery from the battery system. The electronics candisconnect the battery in the event the temperature of the batterysatisfies one or more criteria.

Current interruption devices are often integrated into a battery andinclude a diaphragm that deforms when the pressure in a battery risesabove a threshold. The deformation of the diaphragm disrupts anelectrical connection in the battery and accordingly disconnects thebattery from the battery system.

Suitable battery disconnection devices for addressing undesirablecurrent increases in a battery include fuses. For instances, fuses canbe positioned such that if a battery shorts, the battery is no longer inelectrical communication with the rest of the batteries in the batterysystem 10. Accordingly, the fuses can prevent a cell that shorts in aparallel group from shorting the other cells in the parallel group. Forinstance, the electrical component 34 in FIG. 1C can represent a fusepositioned in series with each of the batteries. Suitable fuses 34include, but are not limited to, traditional fuse devices and bi-metalswitching devices.

An additional or alternative battery disconnection device includes aswitch configured to disconnect a battery from the battery system. Forinstance, a switch can be positioned in series with each of thebatteries. As an example, the electrical components 34 in FIG. 1C caneach represent a switch. Alternately, the electrical components 34 inFIG. 1C can each represent a switch in series with a fuse. Theelectronics can operate the switch. For instance, the electronics canopen and/or close the switch in response to detection of a faultcondition associated with one or more of the batteries. The electronicscan open the switch associated with the faulty battery to effectivelyremove the faulty battery from the battery system. In some instances,the electronics may be able to identify which parallel group includes afaulty battery but is not able to identify which battery in theidentified parallel group is the faulty battery. In these instances, theelectronics can sequentially open and/or close switch associated withdifferent batteries in the identified parallel group. When removing aparticular battery from the battery pack switches halts the faultcondition and/or the operation of the parallel group returns to normal,the switch or combination of switches can be left open. For instance,the electronics may detect that a battery has an internal short when thevoltage of a parallel group drops sharply. However, since each batteryin the parallel group is at the same voltage, the electronics may not beable to identify which battery has shorted. The electronics can opendifferent switches in the parallel group. When opening a switch isfollowed by a stop in the voltage drop, the switch can be left openwhile other switches in the parallel group are left closed. As a result,a portion of the batteries in the identified parallel group can remainfunctioning. Additional or alternate fault conditions that can beidentified by the electronics and remedied by opening one or moreswitches in a parallel group include when one or more batteries has ordevelops an unusually high self-discharge and/or when one or morebatteries has or develops an unusually low capacity and/or when one ormore batteries has or develops an unusually high internal impedance.

The battery system 10 can include other electrical connections betweenthe primary parallel lines 12. For instance, other batteries and/orseries groups can be connected between the primary parallel lines 12 butnot otherwise electrically connected to the illustrated series groups.Further, the battery system 10 can include other components between theprimary parallel lines 12.

The electronics are configured to control the charge and discharge ofthe battery pack. For instance, the electronics can monitor the packcurrent during the charge and/or discharge of the battery pack. Theelectronics can operate the current controller so as to control the packcurrent in response to the monitored pack current. For instance, theelectronics can operate the current controller so as to intermittentlydrop the current from a first current level to a second current level.

FIG. 1D illustrates a possible plot of pack current versus time for adischarging battery pack. The battery pack has a maximum operationalcurrent labeled I_(m). The battery pack also has a recharge currentlabeled I_(R). When the battery pack is at a current less than therecharge current, the batteries in each of the parallel groups rechargeone another and can accordingly achieve the same voltage. When the packassembly 66 is at a current above the recharge current, the batteries ineach of the system parallel groups can not adequately recharge oneanother and differentials between the voltage of different batteries maydevelop. The battery pack also has an intermittent current labeledI_(i). The range of current between the maximum operational current,I_(m), and the intermittent current, I_(i), is labeled a high powerzone. A first current level is between the range of pack currentsbetween the intermittent current I_(i) and the recharge current, I_(R).A second current level is between the range of current between therecharge current, I_(R), and the zero current level or the open circuitcurrent.

At different times during operation of the battery pack 2, the packcurrent will fall between the intermittent current, I_(i), and therecharge current, I_(R). For instance, FIG. 1D shows the pack current atthe first current level in the time periods shown by the bracketslabeled B and D. The electronics are configured such that when the packcurrent falls between the intermittent current, I_(i), and the rechargecurrent, I_(R), the electronics intermittently drop the current to asecond current level. For instance, the dashed lines in FIG. 1Dillustrate the pack current during a drop to a second current level. Thedrop to the second current level provides batteries in the same parallelgroup an opportunity to recharge one another. Although the drop from thefirst current level to the second current level is illustrated as acontinuous drop, the drop can include one or more plateaus between thefirst current level and the second current level.

The drop to the second current level can be a drop to a current level ator below the recharge current, I_(R). In some instances, the secondcurrent level is zero or the open circuit current. When the secondcurrent level is greater than zero or the open circuit current, somecurrent can still be drawn from the battery pack while the batteries inthe parallel groups recharge one another. In some instances, the secondcurrent level is less than zero. A second current level less than zerocan provide additional charging of the batteries above what is achievedwhen the second current level is zero.

The second current level can be different for each drop or for a portionof the drops. For instance, in some instances, the second current levelcan be zero while in other instances, the second current level isgreater than zero. Alternately, the second current level can be the samefor each drop. For instance, the second current level can be zero or theopen circuit current during each of the drops from the first currentlevel to the second current level.

The intermittent drop can be periodic. For instance, the electronics candrop the pack current to a second current level with the same periodbetween drops. Alternately, the drop to a second current level can betriggered by one or more other criteria. For instance, the electronicscan monitor the voltage and/or current of individual batteries. In theevent that the voltage and/or current of one or more batteries risesabove or falls below a threshold, the electronics can drop the packcurrent to the second current level. Alternately or additionally, theelectronics can monitor the voltage and/or current of parallel groups.In the event that the voltage and/or current of one or more parallelgroups rise above or falls below a threshold, the electronics can dropthe pack current to the second current level. As a result, the drop tothe second current level may occur one or more times while charging orwhile discharging.

The duration of the drop to a second current level can be fixed. Forinstance, the duration of the drop to the second current level can bethe same for each time the pack current is dropped to a second currentlevel. Alternately, the duration of the drop can be different fordifferent drops to a second current level. For instance, the duration ofthe drop can be determined in response to one or more criteria. As anexample, the electronics can monitor the voltage and/or current ofindividual batteries. As the voltage differential between differentbatteries in a parallel group increases, the duration of the drop to thesecond current level can be increased.

In some instances, the pack current may increase above the intermittentcurrent, I_(i). For instance, FIG. 1D shows the pack current above theintermittent current, I_(i), in the time period shown by the bracketslabeled C. This situation is most likely to occur during high powerapplications such as acceleration of a vehicle or pulsing applications.When the pack current is above the intermittent current, I_(i), it maynot be desirable to disrupt the current flow from the battery pack. Forinstance, a drop in the current level from the battery pack may cause avehicle to be de-powered during acceleration. As a result, theelectronics can optionally be configured to stop dropping the current tothe second current level when the current rises above the intermittentcurrent, I_(i). In some instances, the intermittent current, I_(i) isset equal to the maximum operational current, I_(m). As a result, theintermittent drop of the current from the first current level to thesecond current level will continue even when the pack is operating at ornear the maximum operational current, I_(m).

In some instances, the pack current may fall below the recharge current,I_(R). For instance, FIG. 1D shows the pack current below the rechargecurrent, I_(R), in the time period shown by the brackets labeled E. Thissituation is likely to occur during low power applications such as occurafter a vehicle has reached a cruising speed. When the pack current isbelow the recharge current, I_(R), it may not be necessary to drop thepack current to the second level since the batteries in the parallelgroups are capable of recharging one another at this level. As a result,when the current falls below the recharge current, I_(R): theelectronics can optionally be configured to stop dropping the packcurrent to the second current level; the duration between the drops tothe second current level can increased; or the electronics can continueto drop the pack current to the second current level according to thesame protocol as was employed when the pack current is above therecharge current, I_(R).

The electrical current provided by the battery pack at the firstterminal 5 and the second terminal 6 need not be disrupted during a dropfrom the first current level to the second current level. For instance,the electronics can be configured to provide the battery pack with acontinuous DC output. As an example, the drops from the first currentlevel to the second current level can be periodic in that the timebetween each drop is the same and the duration of each drop is the same.The electronics can include an AC to DC converter that receives thesignal from the battery system and provides a continuous DC output atthe first terminal 5 and the second terminal 6. When the period betweenthe drops is different from the duration of the drops, an AC to DCconverter configured to handle asymmetric waveforms can provide thedesired output.

During operation of the battery pack, a differential may develop betweenthe voltage of different parallel groups. In some instances, the voltageof one or more parallel groups may rise to levels that are undesirablyhigh or fall to levels that are undesirably low. For instance, thevoltage of one or more parallel groups may rise above a safety thresholdor fall below a safety threshold. In these instances, the electronicscan employ a switch 30 in a shunt circuit 29 to provide a bypass aroundthe failed parallel group. As a result, the failed parallel group iseffectively removed from the battery pack permitting continued operationof the battery pack. When the electronics employ one or more of theshunt circuits, the electronics can adjust one or more other parameters.For instance, the electronics can reduce the voltage to which thebattery pack is charged to prevent over-charging of the battery pack.

The shunt circuits can also be employed in response to other faultcondition in the battery pack. For instance, experiments have shown thata parallel group that includes a battery that has or develops anunusually high self-discharge will contribute to the functioning of thebattery pack for several cycles but subsequent cycling can cause thevoltage of the parallel group to drop to an undesirably low level thatcan adversely affect the performance of the battery pack. Accordingly,the electronics can employ a shunt circuit to bypass a parallel grouponce the voltage of the parallel group falls below a threshold. When theelectronics employ a shunt circuit in response to the voltage of aparallel group falling below a threshold, the shunt circuit ispreferably employed when the voltage of the parallel group is at orbelow the threshold to reduce issues associated with shorting of morehighly charged batteries as a result of employing the shunt circuit. Thethreshold can be higher than the minimum operational voltage of thebatteries in the battery pack. Additionally, the threshold can be higherthan the voltage to which the battery pack is or can be dischargedbefore recharging or is higher than the low voltage of the voltagesbetween which the battery pack is being cycled.

The electronics can include charging electronics for charging thebattery packs 2. The electronics can be configured to recharge each ofthe battery packs 2 individually by applying a potential across thebattery packs 2 individually. Additionally or alternately, thecontroller 64 can be configured to recharge the pack assembly 66 byapplying a potential across the pack assembly 66. Although notillustrated, the controller 64 can include or be attachable to a powersource that provides power for charging the pack assembly 66.

The effects of batteries having different levels of self-discharge,impedance and/or capacity can also cause damage to the battery packduring charging of the battery pack. As a result, the electronics canintermittently drop the pack current from a first current level to asecond current level during the charge of the battery pack. The secondcurrent level can be different for each drop. For instance, in someinstances, the second current level can be zero while in otherinstances, the second current level is greater than zero. Alternately,the second current level can be the same for each drop. For instance,the second current level can be zero or the open circuit current duringeach of the drops from the first current level to the second currentlevel. In some instances, the second current level is less than therecharge current, I_(R), disclosed in the context of FIG. 1D. In someinstances, the second current level is less than zero.

When charging the battery pack, the intermittent drop can be periodic.For instance, the electronics can drop the pack current to a secondcurrent level with the same period between drops. Alternately, the dropto a second current level can be triggered by one or more othercriteria. For instance, the electronics can monitor the voltage and/orcurrent of individual batteries. In the event that the voltage and/orcurrent of one or more batteries rises above or falls below a threshold,the electronics can drop the pack current to the second current level.Alternately or additionally, the electronics can monitor the voltageand/or current of parallel groups. In the event that the voltage and/orcurrent of one or more parallel groups rise above or falls below athreshold, the electronics can drop the pack current to the secondcurrent level.

When charging the battery pack, the duration of the drop to a secondcurrent level can be fixed. For instance, the duration of the drop tothe second current level can be the same for each time the pack currentis dropped to a second current level. Alternately, the duration of thedrop can be different for different drops to a second current level. Forinstance, the duration of the drop can be determined in response to oneor more criteria. As an example, the electronics can monitor the voltageand/or current of individual batteries. As the voltage differentialbetween different batteries in a parallel group increases, the durationof the drop to the second current level can be increased.

Suitable electronics 8 include, but are not limited to, firmware,hardware and software or a combination thereof. Examples of suitableelectronics 8 include, but are not limited to, analog electricalcircuits, digital electrical circuits, processors, microprocessors,digital signal processors (DSPs), computers, microcomputers, ASICs, anddiscrete electrical components, or combinations suitable for performingthe required control functions. In some instances, the electronics 8include one or more memories and one or more processing units such as aCPU. The one or more memories can include instructions to be executed bythe processing unit during performance of the control and monitoringfunctions.

U.S. Provisional Patent Application Ser. No. 60/740,150, filed on Nov.28, 2005, entitled “Battery System Configured To Survive Failure of Oneor More Batteries,” and U.S. patent application Ser. No. 11/501,095,filed on Aug. 8, 2006, entitled “Battery System Configured To SurviveFailure of One or More Batteries,” are each incorporated herein in theirentirety and disclose a method for charging and discharging a batterypack 2 having a battery system 10 constructed according to FIG. 1Athrough FIG. 1C such that the battery pack 2 can survive failure of oneor more batteries without a substantial drop in the capacity in thebattery pack 2. The electronics can charge and discharge the batterypack 2 in accordance with this disclosure in addition to intermittentlydropping the current from the first current level to the second currentlevel.

The battery pack 2 can include electronics in addition to theelectronics 8 illustrated in FIG. 1A through FIG. 1C. For instance, thebattery pack 2 can include electronics 8 for independently monitoringeach of the batteries and/or each of the parallel groups. As a result,the battery pack 2 will require additional connections between theelectronics 8 and the battery system 10 as are needed to provide thedesired functions. For instance, when the voltage of different parallelgroups is monitored, the electronics 8 can employ connections betweenthe parallel lines and the electronics 8 to concurrently monitor voltageof each parallel group. Additionally, the battery pack can includeammeters and/or voltmeters as needed to perform the described functions.

The battery pack 2 can be configured to provide more than 9 V or morethan 12 V. Additionally or alternately, the battery packs 2 can beconfigured to provide more than 50 watt-hours, more than 100 watt-hoursor more than 240 watt-hours. Many of the advantages associated with thebattery pack 2 do not become evident until the battery pack 2 is usedfor applications requiring high power levels. As a result, the batterypack 2 is suitable for high power applications such as powering themovement of vehicles such as trucks, cars and carts. For these highpower applications, the battery pack 2 is preferably configured toprovide more than 18 V, more than 24 V or more than 32 V. Additionallyor alternately, the battery pack 2 is preferably configured to providemore than 240 watt-hours, more than 500 watt-hours or more than 1000watt-hours. In some instances, the above performance levels are achievedusing a battery pack 2 where the batteries in the series groups 14 eachhave a voltage of less than 14 V, 10 V or 5 V.

In some instances, one or more of the batteries are configured toprovide more than 9 V or more than 12 V. Additionally or alternately,the batteries can be configured to provide more than 50 watt-hours, morethan 100 watt-hours or more than 240 watt-hours. When the battery pack 2is used for applications requiring high power levels such as poweringthe movement of vehicles such as trucks, cars and carts, the batteriesare preferably configured to provide more than 18 V, more than 24 V ormore than 32 V. Additionally or alternately, the batteries arepreferably configured to provide more than 240 watt-hours, more than 500watt-hours or more than 1000 watt-hours.

FIG. 2A is a schematic of a battery pack system 42. The battery packsystem 42 includes a controller 64 in electrical communication with apack assembly 66. The pack assembly includes a plurality of batterypacks. All or a portion of the battery packs can be constructedaccording to FIG. 1A through FIG. 1D. Alternately, different batterypack constructions can be employed. Alternately, the battery packs canhave battery systems according to FIG. 1A through FIG. 1C but can employelectronics with different functions or can exclude electronicsaltogether.

The pack assembly 66 includes two primary parallel conductors 68 thatconnect three system series groups 70 in parallel. The system seriesgroups 70 each include three battery packs 2 connected in series.Primary series conductors 72 each provide electrical communicationbetween a system series group 70 and a primary parallel conductor 68 andsecondary series conductors 74 provide electrical communication betweenthe battery packs 2 connected in series.

The pack assembly 66 also includes a plurality of secondary parallelconductors 76. The secondary parallel conductors 76 each include one ormore cross conductors 78 that provide electrical communication betweenthe secondary series conductors 74 in different system series groups 70.Accordingly, each secondary parallel conductor 76 provides a parallelconnection between the battery packs 2 in different system series group70. For instance, each secondary parallel conductor 76 provideselectrical communication between different system series groups 70 suchthat a battery pack 2 in one of the system series groups 70 is connectedin parallel with a battery pack 2 in the other system series groups 70.Because a single secondary parallel conductor 76 only provides one ofthe parallel connections, another connection is needed to connectbattery packs 2 in parallel. The other parallel connection can beprovided by another secondary parallel conductor 76 or by a primaryparallel conductor 68. Each of the battery packs 2 connected in parallelbelongs to a system parallel group 80. Accordingly, the pack assembly 66of FIG. 2A includes three system parallel groups 80. As is evident fromthe discussion of FIG. 1B, the battery assembly of FIG. 2A can also beillustrated as a plurality of system parallel groups connected inseries.

The pack assembly 66 of FIG. 2A can be scaled to include more batterypacks 2 or fewer battery packs 2. For instance, the system can includefour or more battery packs 2, twelve or more battery packs 2,twenty-five or more battery packs 2, eighty-one or more battery packs 2,one hundred or more battery packs 2. The number of battery packs 2 ineach system parallel group 80 can be the same or different from thenumber of battery packs 2 in each system series group 70. The number ofbattery packs 2 in each system series group 70 can be increased in orderto increase the voltage of the system or decreased in order to decreasethe voltage of the system. Each system series group 70 can include twoor more battery packs 2; four or more battery packs 2; more than eightbattery packs 2; or fifteen or more battery packs 2. The number ofsystem series groups 70 can be increased for applications that requirehigher power levels or decreased for applications that require lowerpower levels. In some instances, the pack assembly 66 includes one ormore system series groups 70 and one or more system parallel groups. Inone embodiment, the pack assembly includes only one system parallelgroup and no series groups. The pack assembly can include two or moresystem series groups 70; four or more system series groups 70; ten ormore system series groups 70; or fifteen or more system series groups70.

Although FIG. 2A illustrates the secondary parallel conductors 76providing electrical communication between the system series groups 70such that a battery pack 2 in one of the system series groups 70 isconnected in parallel with a battery pack 2 in each of the other systemseries groups 70, the secondary parallel conductors 76 can provideelectrical communication between the system series groups 70 such that abattery pack 2 in one of the system series groups 70 is connected inparallel with a battery pack 2 in a portion of the other system seriesgroups 70.

The pack assembly 66 can include electrical connections between theprimary parallel conductors 68 other than the electrical connectionsshown in FIG. 2A. For instance, other battery packs 2 and/or systemseries groups 70 can be connected between the primary parallelconductors 68 but not otherwise electrically connected to theillustrated system series groups 70. Further, the pack assembly 66 caninclude other components. For instance, the pack assembly 66 can includefuses positioned such that if a battery pack 2 shorts, the battery pack2 is no longer in electrical communication with the rest of the batterypacks 2 in the pack assembly 66. For instance, a fuse can be associatedwith each battery pack 2 and placed in series with the associatedbattery pack 2. Accordingly, the fuses can prevent a battery pack 2 thatshorts in a system parallel group 80 from shorting the other batterypack 2 in the system parallel group 80. Suitable fuses include, but arenot limited to, traditional fuse devices and bi-metal switching devices

The pack assembly can include a plurality of switches that are eachconfigured to disconnect a battery pack from the pack assembly. Forinstance, a switch can be associated and placed in series with eachbattery pack 2. In some instances, each switch is also connected inseries with a fuse such that a fuse, switch, and battery pack are allconnected in series. The controller can operate the switches. Forinstance, the controller can open and/or close the switch in response todetection of a fault condition associated with one or more of thebattery packs. The controller can open the switch associated with thefaulty battery pack to effectively remove the faulty battery pack fromthe pack assembly. In some instances, the controller may be able toidentify which system parallel group includes a faulty battery pack butis not able to identify which battery pack in the identified systemparallel group is the faulty battery pack. In these instances, thecontroller can sequentially open and/or close switches associated withdifferent batteries in the identified parallel group. When removing aparticular battery pack from the pack assembly halts the fault conditionand/or the operation of the system parallel group returns to normal, theswitch or combination of switches can be left in the condition thatassociated with the removal of that battery pack from the pack assembly.For instance, the controller may detect that a battery pack has aninternal short when the voltage of a system parallel group dropssharply. However, since each battery pack in the system parallel groupis at the same voltage, the controller may not be able to identify whichbattery pack has shorted. The controller can open different switches inthe system parallel group. When opening a switch is followed by a stopin the voltage drop, the switch can be left open while other switches inthe system parallel group are left closed. As a result, a portion of thebattery packs in the identified system parallel group can remainfunctioning. Additional or alternate fault conditions that can beidentified by the controller and remedied by opening one or moreswitches in a system parallel group include when one or more batterypacks has or develops an unusually high self-discharge and/or when oneor more battery packs has or develops an unusually low capacity and/orwhen one or more battery packs has or develops an unusually highinternal impedance.

The pack assembly 66 can include one or more shunt circuits connected inparallel with a system parallel group. A shunt circuit can include oneor more switches and one or more resistors. For instance, the packassembly 66 of FIG. 2A includes a plurality of shunt circuits 82 thatare each configured to provide a current pathway around a systemparallel group. Each shunt circuit 82 includes a switch 84 connected inseries with a resistor 85. The switches can be operated by theelectronics. Each switch 84 is arranged such that one of the systemparallel groups is shorted when the switch is closed and but the shuntcircuit is an open circuit when the switch is open. Accordingly, thesystem parallel group is not shorted when switch is open. When a switchis closed, the associated resistor is selected to prevent thefunctioning batteries in the bypassed system parallel group from beingshort circuited.

The controller includes a current controller 86 for controlling the packcurrent. For instance, the controller can include a pulse generatorconfigured to generate a pulse signal that intermittently drops the packcurrent from the first current level to the second current level. In oneexample, the current controller includes one or more switches that dropthe pack current to a zero current or an open circuit current when theswitch is open. Closing the switch can return the pack current to thefirst current level. The switch can be opened and closed tointermittently drop the current to the second current level. In anotherexample, the current controller can include a switch in parallel withone or more resistors including variable resistors. When the switch isopen the pack current will be dropped to a current limited by the one ormore resistors. The resistors can be adjusted such that when the switchis open, the pack current is dropped to a second current level. When theswitch is open, the one or more resistors are bypassed and the packcurrent rises to the first current level.

The controller is configured to control the charge and discharge of thepack assembly 66. For instance, the controller can monitor the systemcurrent during the charge and/or discharge of the pack assembly 66. Thecontroller can operate the current controller 86 so as to control thesystem current in response to the monitored system current. Forinstance, the controller can operate the current controller 86 so as tointermittently drop the current from a first current level to a secondcurrent level in response to the monitored system current falling withina predetermined range.

FIG. 2C illustrates a possible plot of system current versus time for apack assembly 66 during discharge of the pack assembly 66. The packassembly 66 has a maximum operational current labeled I_(m). The packassembly 66 also has a recharge current labeled I_(R). When the packassembly 66 is at a current less than the recharge current, the batterypacks in each of the system parallel groups recharge one another and canaccordingly achieve the same voltage. When the pack assembly 66 is at acurrent above the recharge current, the battery packs in each of thesystem parallel groups can not adequately recharge one another anddifferentials between the voltage of different packs may develop. Thepack assembly 66 also has an intermittent current labeled I_(i). Therange of system currents between the maximum operational current, I_(m),and the intermittent current, I_(i), is labeled a high power zone. Afirst current level is in the range of system currents from theintermittent current I_(i) to the recharge current, I_(R). A secondcurrent level is in the range of system currents from the rechargecurrent, I_(R), and the zero current level or the open circuit current.

At various times during operation of the pack assembly 66, the systemcurrent will fall between the intermittent current, I_(i), and therecharge current, I_(R). For instance, FIG. 1D shows the system currentat the first current level in the time periods shown by the bracketslabeled B and D. The controller is configured such that when the systemcurrent falls between the intermittent current, I_(i), and the rechargecurrent, I_(R), the controller intermittently drop the current to thesecond current level. For instance, the dashed lines in FIG. 2Cillustrate the system current during a drop to a second current level.The drop to the second current level provides battery packs in the samesystem parallel group an opportunity to recharge one another. Althoughthe drop from the first current level to the second current level isillustrated as a continuous drop, the drop can include one or moreplateaus between the first current level and the second current level.

The drop to the second current level can be a drop to a current level ator below the recharge current, I_(R). In some instances, the secondcurrent level is zero or the open circuit current. When the secondcurrent level is greater than zero or the open circuit current, somecurrent can still be drawn from the pack assembly while the batterypacks in the system parallel groups recharge one another. In someinstances, the second current level is less than zero. A second currentlevel less than zero can provide additional charging of the batteriesabove what is achieved when the second current level is zero.

The second current level can be different for each drop. For instance,in some instances, the second current level can be zero while in otherinstances, the second current level is greater than zero. Alternately,the second current level can be the same for each drop. For instance,the second current level can be zero or the open circuit current duringeach of the drops from the first current level to the second currentlevel.

The intermittent drop can be periodic. For instance, the controller candrop the system current to a second current level with the same periodbetween drops. Alternately, the drop to a second current level can betriggered by one or more other criteria. For instance, the controllercan monitor the voltage and/or current of individual battery packs. Inthe event that the voltage and/or current of one or more batter packsrises above or falls below a threshold, the controller can drop thesystem current to the second current level. Alternately or additionally,the controller can monitor the voltage and/or current of system parallelgroups. In the event that the voltage and/or current of one or moresystem parallel groups rise above and/or falls below a threshold, thecontroller can drop the system current to the second current level. As aresult, the drop to the second current level may occur one or more timeswhile charging or while discharging.

The duration of the drop to a second current level can be fixed. Forinstance, the duration of the drop to the second current level can bethe same for each time the system current is dropped to a second currentlevel. Alternately, the duration of the drop can be different fordifferent drops to a second current level. For instance, the duration ofthe drop can be determined in response to one or more criteria. As anexample, the controller can monitor the voltage and/or current ofindividual battery packs. As the voltage differential between differentbattery packs in a system parallel group increases, the duration of thedrop to the second current level can be increased.

In some instances, the system current may increase above theintermittent current, I_(i) into the high power zone. For instance, FIG.1D shows the system current above the intermittent current, I_(i), inthe time period shown by the brackets labeled C. This situation is mostlikely to occur during high power applications such as acceleration of avehicle or pulsing applications. When the system current is above theintermittent current, I_(i), it may not be desirable to disrupt thecurrent flow from the pack assembly. For instance, a drop in the currentlevel from the pack assembly may cause a vehicle to be de-powered duringacceleration. As a result, the controller can optionally be configuredto stop dropping the current to the second current level when thecurrent rises above the intermittent current, I_(i). In some instances,the intermittent current, I_(i) is set equal to the maximum operationalcurrent, I_(m). As a result, the intermittent drop of the current fromthe first current level to the second current level will continue evenwhen the pack is operating at or near the maximum operational current,I_(m).

In some instances, the system current may fall below the rechargecurrent, I_(R). For instance, FIG. 1D shows the system current below therecharge current, I_(R), in the time period shown by the bracketslabeled E. This situation is likely to occur during low powerapplications such as occur after a vehicle has reached a cruising speed.When the system current is below the recharge current, I_(R), it may notbe necessary to drop the system current to the second level since thebattery packs in the system parallel groups are capable of rechargingone another at this level. As a result, when the current falls below therecharge current, I_(R): the controller can optionally be configured tostop dropping the system current to the second current level; theduration between the drops to the second current level can increased; orthe controller can continue to drop the system current to the secondcurrent level according to the same protocol as was employed when thesystem current is above the recharge current, I_(R).

The electrical current provided by the battery pack system at theterminals 46 need not be disrupted during a drop from the first currentlevel to the second current level. For instance, the electronics can beconfigured to provide the battery pack with a continuous DC output. Asan example, the drops from the first current level to the second currentlevel can be periodic in that the time between each the drops isconstant and the duration of each drop is constant. The electronics caninclude an AC to DC converter that receives the signal from the batterysystem and provides a continuous DC output at the first terminal 5 andthe second terminal 6. When the period between the drops is differentfrom the duration of the drops, an AC to DC converter can be configuredto handle asymmetric waveforms can provide the desired output.

During operation of the pack assembly, a differential may developbetween the voltage of different system parallel groups. In someinstances, the voltage of one or more system parallel groups may rise tolevels that are undesirably high or fall to levels that are undesirablylow. For instance, the voltage of one or more system parallel groups mayrise above a safety threshold or fall below a safety threshold. In theseinstances, the controller can employ a switch 84 in a shunt circuit 82to provide a short around the failed system parallel group. As a result,the failed system parallel group is effectively removed from the packassembly permitting continued operation of the pack assembly. When thecontroller employs one or more of the shunt circuits, the controller canadjust one or more other parameters. For instance, the controller canreduce the voltage to which the pack assembly is charged to preventover-charging of the pack assembly.

The shunt circuits can also be employed in response to other faultcondition in the battery pack assembly. For instance, a system parallelgroup that includes a battery pack that has or develops an unusuallyhigh self-discharge may contribute to the functioning of the batterypack for several cycles but subsequent cycling may cause the voltage ofthe system parallel group to drop to an undesirably low level that canadversely affect the performance of the battery pack assembly.Accordingly, the controller can employ a shunt circuit to bypass asystem parallel group once the voltage of the system parallel groupfalls below a threshold. When the controller employs a shunt circuit inresponse to the voltage of a parallel group falling below a threshold,the shunt circuit is preferably employed when the voltage of theparallel group is at or below the threshold to reduce the issuesassociated with shorting of more highly charged batteries as a result ofemploying the shunt circuit. The threshold can be higher than theminimum operational voltage of the battery packs in the pack assembly.Additionally, the threshold can be higher than the voltage to which thepack assembly is or can be discharged before recharging or is higherthan the low voltage of the voltages between which the battery packassembly is being cycled.

The controller 64 can include charging electronics for charging thebattery packs 2. The controller 64 can be configured to recharge each ofthe battery packs 2 individually by applying a potential across thebattery packs 2 individually. Additionally or alternately, thecontroller 64 can be configured to recharge the pack assembly 66 byapplying a potential across the pack assembly 66. Although notillustrated, the controller 64 can include or be attachable to a powersource that provides power for charging the pack assembly 66.

The effects of batteries having different levels of self-discharge,impedance and/or capacity can also cause damage to the pack assemblyduring charging of the battery pack. As a result, the electronics canintermittently drop the pack current from a first current level to asecond current level during the charge of the battery pack. The secondcurrent level can be different for each drop. For instance, in someinstances, the second current level can be zero while in otherinstances, the second current level is greater than zero. Alternately,the second current level can be the same for each drop. For instance,the second current level can be zero or the open circuit current duringeach of the drops from the first current level to the second currentlevel. In some instances, the second current level is less than therecharge current, I_(R), disclosed in the context of FIG. 2C. In someinstances, the second current level is less than zero.

When charging the pack assembly, the intermittent drop can be periodic.For instance, the controller can drop the system current to a secondcurrent level with the same period between drops. Alternately, the dropto a second current level can be triggered by one or more othercriteria. For instance, the controller can monitor the voltage and/orcurrent of individual battery packs. In the event that the voltageand/or current of one or more battery packs rises above or falls below athreshold, the controller can drop the system current to the secondcurrent level. Alternately or additionally, the controller can monitorthe voltage and/or current of system parallel groups. In the event thatthe voltage and/or current of one or more system parallel groups riseabove or falls below a threshold, the controller can drop the systemcurrent to the second current level.

When charging the pack assembly, the duration of the drop to a secondcurrent level can be fixed. For instance, the duration of the drop tothe second current level can be the same for each time the pack currentis dropped to a second current level. Alternately, the duration of thedrop can be different for different drops to a second current level. Forinstance, the duration of the drop can be determined in response to oneor more criteria. As an example, the controller can monitor the voltageand/or current of individual batteries. As the voltage differentialbetween different batteries in a parallel group increases, the durationof the drop to the second current level can be increased.

U.S. Provisional Patent Application Ser. No. 60/740,150, filed on Nov.28, 2005, entitled “Battery System Configured To Survive Failure of Oneor More Batteries,” and U.S. patent application Ser. No. 11/501,095,filed on Aug. 8, 2006, entitled “Battery System Configured To SurviveFailure of One or More Batteries,” are each incorporated herein in theirentirety and disclose a method for charging and discharging a batterypack 2 having a battery system 10 constructed according to FIG. 1Athrough FIG. 1C such that the battery pack 2 can survive failure of oneor more batteries without a substantial drop in the capacity in thebattery pack 2. The disclosure of this Patent Application can be adaptedto charging and discharging the pack assembly 66. As a result, thecontroller 64 can charge and discharge a pack assembly 66 in accordancewith this disclosure in addition to intermittently dropping the currentfrom the first current level to the second current level.

The battery pack system 42 can include electronics in addition to theelectronics illustrated in FIG. 2A. For instance, the battery packsystem 42 can include electronics for charging the pack assembly 66 byapplying a potential across the pack assembly 66. As a result, thebattery pack system 42 may require additional connections between thecontroller 64 and the pack assembly 66. Additionally, the battery packassembly 42 can include ammeters and/or voltmeters as needed to performthe described functions.

Suitable controllers 64 can include firmware, hardware and software or acombination thereof. Examples of suitable controllers 64 include, butare not limited to, analog electrical circuits, digital electricalcircuits, processors, microprocessors, digital signal processors (DSPs),computers, microcomputers, ASICs, and discrete electrical components, orcombinations suitable for performing the required control functions. Insome instances, the controller 64 includes one or more memories and oneor more processing units such as a CPU. The one or more memories caninclude instructions to be executed by the processing unit duringperformance of the control and monitoring functions.

In some instances, the battery packs 2 in a pack assembly 66 can bedifferent from one another. For instance, a portion of the battery packs2 can be high power sources and a portion of the battery packs 2 can below power sources. In one example, the battery pack assembly includesonly one system parallel group that includes one or more high powersources and one or more low power sources. A high power source has amass based power density (gravimetric power density) that is more thanthe mass based power density of the low power sources. Additionally oralternately, the low power sources can have an impedance that is morethan three times the impedance of the high power sources. Additionallyor alternately, a low power source can have a capacity that is more thanthe capacity of a high power source. In some instances, the high powersources have a mass based power density that is more than twice the massbased power density of the low power sources before discharge of thepack assembly or that is more than four times the mass based powerdensity of the low power sources before discharge of the pack assembly.Additionally or alternately, in some instances, at least one low powersource has a capacity that is greater than a capacity of at least onehigh power source or that is greater than 1.2 times the capacity of atleast one high power source.

Each system parallel group 80 can include one or more high power sourcesand one or more low power sources. The battery packs 2 can be arrangedsuch that one or more system series groups 70 include only high powersources and one or more system series groups 70 include only low powersources. For instance, FIG. 2B is a schematic for a pack assembly 66with one system series group 70 that employs only high power sources asillustrated by the battery packs 2 labeled H and two system seriesgroups 70 that employ only low power sources as illustrated by thebattery packs 2 labeled L. In one example, the pack assembly 66 has onlyone parallel group that includes one or more high power sources and oneor more low power sources. Since the high power sources can have a massbased power density that is more than the mass based power density ofthe low power sources and the low power sources can have an impedancethat is more than the impedance of the high power sources, the currentcan flow primarily from the high power sources during high powerapplications such as pulsing. When the power demands on the packassembly drops, the portion of the current provided by the low powersources increases. During the high power application, the low powersources will have discharged less energy than the high power sources. Asa result, the high power sources will be associated with a highervoltage drop than the low power sources. However, because the parallellines maintain the power sources in the same parallel group at the samevoltage, the low power sources will recharge the high power sources.This arrangement permits the battery assembly to repeatedly satisfy therequirements of high power applications and low power applications.

Additional details about the construction, operation, and/or electronicsfor a battery pack 2 and battery pack systems 42 can be found in U.S.Provisional Patent Application Ser. No. 60/601,285; filed on Aug. 13,2004; entitled “Battery Pack;” and in U.S. patent application Ser. No.11/201,987; filed on Aug. 10, 2005; and entitled “Battery Pack;” and inU.S. Patent Application Ser. No. 60/707,500; filed on Aug. 10, 2005; andentitled “Battery System;” and in U.S. Patent Application Ser. No.60/740,150; filed on Nov. 28, 2005; and entitled “Battery SystemConfigured to Survive Failure of One or More Batteries;” and in U.S.patent application Ser. No. 11/501,095, filed on Aug. 8, 2006, entitled“Battery System Configured To Survive Failure of One or More Batteries;”and in U.S. Patent Application Ser. No. 60/740,204; filed on Nov. 28,2005; and entitled “Battery Pack System;” and in U.S. Patent ApplicationSer. No. 60/740,202; filed on Nov. 28, 2005; and entitled “Battery PackSystem;” and in U.S. patent application Ser. No. 11/269,285; filed onNov. 8, 2005; and entitled “Modular Battery Pack;” each of which isincorporated herein in its entirety. When possible, the functions of theelectronics and/or controllers described in the above applications canbe performed in addition to the functions described in this application.

Although the function of the electronics 8 of FIG. 1A and the controller64 of FIG. 2A are described separately, in many instances, all or aportion of the electronics functions are incorporated into thecontroller. Accordingly, in some instances, the battery packs canexclude the electronics 8. Alternately, all or a portion of thecontroller functions can be incorporated into the electronics.

The battery pack system 42 can be employed to power movement of avehicle. Examples of suitable vehicles are vehicles configured to holdand transport living people such as cars, truck and golf-carts. In someinstances, the vehicles are for transporting people on land. FIG. 3illustrates a battery pack system 42 employed in a vehicle 92. Thebattery pack system 42 provides an electrical signal to a power source94 which is connected to a power train 96. The power train is configuredto transmit power from the power source to a drive mechanism (not shown)such as a drive axel. The power source can include a motor and/orengine. The battery system can assist the motor and/or engine ingenerating movement of the vehicle 92. Alternately, the battery systemcan be the only source of power provided to the power source. Althoughthe battery pack system 42 is disclosed in the context of a battery forpowering vehicles, the battery pack system 42 can be employed in otherapplications.

Other embodiments, combinations and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. Therefore, this invention is to be limited only by thefollowing claims, which include all such embodiments and modificationswhen viewed in conjunction with the above specification and accompanyingdrawings.

1. A battery pack system, comprising: a battery pack including aplurality of parallel groups connected in series, each parallel groupincluding a plurality of batteries connected in parallel; andelectronics configured to charge the battery pack at a first currentlevel and to drop the current from the first current level to a secondcurrent level one or more times while charging the battery pack, thesecond current level being lower than the first current level.
 2. Thesystem of claim 1, wherein the electronics are configured to drop thecurrent from the first current level to a second current level at aregular interval.
 3. The system of claim 1, wherein a time period overwhich the current is dropped to the second current level is constant foreach event where the current is dropped to the second current level. 4.The system of claim 1, wherein the first current level is a currentlevel required to charge the battery pack.
 5. The system of claim 1,wherein the second current level is an open circuit current level forthe battery pack.
 6. The system of claim 1, wherein the second currentlevel is below a recharge current at which the batteries in a parallelgroup are able to recharge other batteries in the same parallel group.7. The system of claim 1, wherein the battery pack is one of a pluralityof battery packs, each of the battery packs connected in a plurality ofsystem parallel groups that are connected in series, each systemparallel group including a plurality of battery packs connected inparallel.
 8. A battery pack system, comprising: a plurality of systemparallel groups connected in series, each system parallel groupincluding a plurality of battery packs connected in parallel; eachbattery pack including a plurality of parallel groups connected inseries, each parallel group including a plurality of batteries connectedin parallel; electronics configured to charge the battery packs at afirst current level and to drop the current from the first current levelto a second current level one or more time while charging the batterypacks, the second current level being lower than the first currentlevel; the electronics being configured to stop intermittently droppingthe current from the first current level to the second current levelwhen the first current level rises above an upper current threshold; andthe electronics being configured to stop intermittently dropping thecurrent from the first current level to the second current level whenthe first current level falls below a lower current threshold.
 9. Abattery pack system, comprising: a pack assembly having a plurality ofsystem parallel groups connected in series, each system parallel groupincluding a plurality of battery packs connected in parallel;electronics configured to charge the pack assembly at a first currentlevel and to intermittently drop the current from the first currentlevel to a second current level while charging the pack assembly, thesecond current level being lower than the first current level.
 10. Thesystem of claim 9, wherein the electronics are configured to drop thecurrent from the first current level to a second current level at aregular time interval.
 11. The system of claim 9, wherein a time periodover which the current is dropped to the second current level isconstant for each event where the current is dropped to the secondcurrent level.
 12. The system of claim 9, wherein the first currentlevel is a current level required to charge the pack assembly.
 13. Thesystem of claim 9, wherein the second current level is an open circuitcurrent level for the pack assembly.
 14. The system of claim 9, whereinthe second current level is below a recharge current at which thebattery packs in a system parallel group are able to recharge otherbatteries in the same system parallel group.
 15. A battery pack system,comprising: a battery pack including a plurality of parallel groupsconnected in series, each parallel group including a plurality ofbatteries connected in parallel; electronics configured to dischargeand/or charge the battery pack; and one or more shunt circuitsconfigured to bypass one or more of the parallel groups, the shuntcircuits being activated by the electronics.
 16. A battery pack system,comprising: a pack assembly having a plurality of system parallel groupsconnected in series, each system parallel group including a plurality ofbattery packs connected in parallel; electronics configured to chargeand/or discharge the pack assembly; and one or more shunt circuitsconfigured to bypass one or more of the system parallel groups, theshunt circuits being activated by the electronics.
 17. A battery packsystem, comprising: a battery pack including a plurality of parallelgroups connected in series, each parallel group including a plurality ofbatteries connected in parallel; electronics configured to dischargeand/or charge the battery pack; and a switch connected in series withone or more batteries, the switch being operated by the electronics. 18.The system of claim 17, wherein the electronics are configured to open aswitch connected in series with a battery in response to detecting afault condition at that battery.
 19. A battery pack system, comprising:a pack assembly having a plurality of system parallel groups connectedin series, each system parallel group including a plurality of batterypacks connected in parallel; electronics configured to charge and/ordischarge the pack assembly; and a switch connected in series with oneor more battery pack, the switch being operated by the electronics. 20.The system of claim 19, wherein the electronics are configured to open aswitch connected in series with a battery pack in response to detectinga fault condition at that battery pack.